Critical Behavior Near the Ferromagnetic Transition in Nanostructured Gadolinium

ac susceptibility and dc magnetization have been measured near the ferromagnetic transition in melt-spun nanostructured Gd. Effective critical exponents and the critical temperature were extracted using modified Arrott plots. The values obtained were \textit{$\beta $}$_{eff}$ = 0.415 $\pm $ 0.005, \textit{$\gamma $}$_{ eff}$ = 1.36 $\pm $ 0.04, \textit{$\delta $}$_{ eff}$ = 4.24 $\pm $ 0.02, and $T_{C}$ = 290.0 $\pm $ 0.1 K. These exponent values satisfy the scaling relation \textit{$\beta \delta $ }= (\textit{$\beta $}+\textit{$\gamma $}). The experimental exponent values are also close to those for a short-range 3D Heisenberg ferromagnet; however, there is a systematic shift toward mean-field values. Such a shift has been previously seen in amorphous ferromagnets and is likely due to the presence of longer-ranged interactions, especially in Gd-based alloys. The critical exponents for nanostructured Gd are closer to the short-range 3D Heisenberg exponents than are those for amorphous Gd$_{67}$Co$_{33}$ and Gd$_{80}$Au$_{20}$. This suggests that the dominant Gd-Gd interactions are shorter-ranged in nanostructured Gd than in the amorphous alloys.